使用Reader Monad进行依赖注入 [英] Using Reader Monad for Dependency Injection

问题描述

我最近看到死亡简单依赖注入和没有体操的依赖注射关于DI与Monads的DIY并且印象深刻。我试图将其应用于一个简单的问题，但一旦遇到不便，就失败。我真的想看到依赖注入的运行版本，其中

I recently saw the talks Dead-Simple Dependency Injection and Dependency Injection Without the Gymnastics about DI with Monads and was impressed. I tried to apply it on a simple problem, but failed as soon as it got non-trivial. I really would like to see a running version of dependency injection where

• 依赖于多个值必须注入的类


• 一个依赖于依赖于要注入的东西的类的类

以下示例

trait FlyBehaviour { def fly() }
trait QuackBehaviour { def quack() }
trait Animal { def makeSound() }

// needs two behaviours injected
class Duck(val flyBehaviour: FlyBehaviour, val quackBehaviour: QuackBehaviour) extends Animal 
{
   def quack() = quackBehaviour.quack()
   def fly() = flyBehaviour.fly()
   def makeSound() = quack()
}

// needs an Animal injected (e.g. a Duck)
class Zoo(val animal: Animal)

// Spring for example would be able to provide a Zoo instance
// assuming a Zoo in configured to get a Duck injected and
// a Duck is configured to get impl. of FlyBehaviour and QuackBehaviour injected
val zoo: Zoo = InjectionFramework.get("Zoo")
zoo.animal.makeSound()

使用读者Monad查看示例实现真的很有帮助，因为我只是觉得我错过了正确的方向。

It would be really helpful to see a sample implementation using the reader Monad since I just feel that I am missing a push in the right direction.

谢谢！

推荐答案

reader monad只是 Function1 ，所以你需要做的是接受一个包含所有你需要的东西的参数。例如：

The "reader monad" is just Function1, so all you need to do is accept an argument containing all the things you need. For example:

trait Config {
   def fly: FlyBehaviour
   def quack: QuackBehaviour
}

type Env[A] = Config => A

现在，如果你想构建一个 Duck 基于这种环境：

Now if you want to construct a Duck based on this environment:

val a: Env[Animal] = c => new Duck(c.fly, c.quack)

然后构建一个动物园根据这个很容易：

And then constructing a Zoo based on that is easy:

val z: Env[Zoo] = a andThen (new Zoo(_))

使用 Scalaz （或者你自己的一些工作），你可以利用一些语法细节来询问配置 c ：

Using Scalaz (or with a bit of work on your own) you can make use of some syntax niceties to "ask" for the config c:

val z: Env[Zoo] = for {
  c <- ask
} yield new Zoo(Duck(c.fly, c.quack))

这篇关于使用Reader Monad进行依赖注入的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！